3-Methylindole (3MI) is an anaerobic bacterial fermentation product of tryptophan that is produced in the rumen and large intestine of animals. 3MI is a constituent of cigarette smoke. 3MI causes acute pulmonary edema and interstitial emphysema in cattle, goats, sheep and mice and small airways disease in horses. Its effects are rapid and cellular specific with most severe damage to type 1 alevolar and non-ciliated bronchiolar epithelial (Clara) cells. 3MI is rapidly metabolized and at least 10 end products are excreted in the urine. Lung injury results from cytochrome P-450 metabolism of 3MI and the presence of covalently bound metabolites suggests that reactive intermediates are formed during metabolism. The overall goal of this project is to determine the mechanism of 3MI-induced acute lung injury, explain the reasons for cellular, organ and species differences in 3MI toxicity and to evaluate the risk of exposure to 3MI in man. To accomplish this, we plan to correlate covalent binding and pathological changes in lung cells, organs and species. Glutathione conjugation, antioxidants and radical scavengers will be used to characterize the chemical nature of the reactive intermediate. Reactive intermediates will be trapped and isolated and the structures of the adducts will be determined. Deuterium-labelled analogs of 3MI will be synthesized and used to assess the nature of the toxic intermediates. In addition, we plan to investigate the microbiology and enzymology associated with 3MI formation. These studies represent a biochemical, toxicological, chemical and pathological investigation of a chemically-induced acute lung injury responsible for naturally-occurring disease in ruminants and with unknown effects in other species, including man.